What acute condition is associated with muddy brown casts in urine?

The presence of muddy brown casts in urine is classically associated with acute tubular necrosis (ATN). In ATN, the epithelial cells of the renal tubules undergo injury, which leads to the sloughing of these cells into the tubular lumen. As these necrotic cells collect in the urine, they form identifiable casts that appear muddy brown under the microscope. This is a hallmark finding for ATN and helps differentiate it from other forms of renal dysfunction.

Acute glomerulonephritis typically shows red blood cells and red blood cell casts in the urine due to glomerular inflammation. Acute interstitial nephritis is characterized by white blood cells and sometimes eosinophils in the urine rather than muddy brown casts. Acute pyelonephritis often presents with WBC casts or bacteria but not muddy brown casts. Therefore, muddy brown casts are a specific indicator of cellular damage and necrosis occurring in the tubules, which is why acute tubular necrosis is the correct association in this context.